The Washington State Department of Transportation is rushing to put in place a temporary bridge to restore traffic across I-5 at the Skagit River and is fast-tracking a permanent replacement.

Most states don't want a gaping hole in their major interstate disrupting the traffic of roughly 71,000 daily vehicles—one so prominent even Google Maps takes notice. Now that the emergency response to the destruction of the I-5 bridge over the Skagit River in Washington State is past, officials at the Washington State Department of Transportation (WSDOT) are racing to put in a temporary span to restore interstate traffic, as well as developing a fast-tracked permanent fix.

Temporary Bridge

Fortunately for WSDOT, the Skagit River crossing isn't a tricky site, and preliminary reports show that the bridge was not damaged beyond the 160 feet that fell into the water. With the in-water concrete piers in fine shape and the other three spans of the 1111-foot bridge in good-enough condition, the basic foundation is already in place for a temporary fix. That means a temporary bridge could be carrying cars by mid-June, a mere three weeks after the bridge came crashing down and less than two weeks after debris is fully removed from the site, which is ongoing this week.

The temporary fix will include two 160-foot-long spans, both 24 feet wide (narrower than the rest of the bridge). It's a modern riff on the Bailey bridge—a temporary bridge style made popular in World War II for its modular ease of build and lightweight steel—that will allow for quick assembly on-site. The Bailey was popular during the war because it was light enough to haul by truck and use manpower to lift small segments. New Jersey–based Acrow Bridges has taken this mid-1900s wartime tool and turned it into a modern—and worldwide—business, showcased by bridges from Chile to the World Trade Center site in New York.

Acrow already has shipped temporary parts to Mount Vernon, Wash., on the southern bank of the Skagit River. Using steel trusses and modular construction units that fit on trucks for quick transport, crews will splice together this prefabricated bridge in a matter of days. During construction, crews can cantilever the pieces in place from one side of the river or use cranes to place the segments. If they need more length, they simply add another component. That's how easy these premade bridges are.

The narrow lanes and lightweight structure will limit the size and weight of crossing vehicles and require slower speeds over the spans, but at least the bridge will give detour routes a bit of a breather. Then comes the permanent fix.

Fast-Tracking a Permanent Bridge

As cars begin driving the temp bridge this summer, crews will be building a permanent replacement in the river right next to the temporary structure. This type of bridge construction has become common, as new bridges can replace old ones in a matter of days when constructed off-site or nearby and then simply moved into place. Scott Nettleton, a T.Y. Lin senior bridge engineer, says accelerated bridge construction has turned into another design tool.

In Washington State plans haven't been finalized. Crews expect to build temporary piers in the river to support a platform adjacent to the collapsed span. That's where you'll see a new bridge section built. The new bridge will be a steel girder, a style that offers structural support below the bridge deck and not in a web above and to the side like the way the rest of the Skagit River bridge is built. The new Skagit section will use steel rather than concrete to make the bridge lighter, putting less strain on the 1955-built concrete piers. Plus, girders take much less time to construct than complicated truss styles.

Once the fully assembled bridge is set, crews will remove the temporary bridge and use beams and giant rollers to slowly scoot the new structure onto the old foundation. Once in place—and after some final intricate positioning—the translator beams and temporary river supports will get removed.

Residents throughout the West have seen dozens upon dozens of fast-tracked bridges go up in recent years, especially in Utah where accelerated construction is the norm. In nonemergency situations, crews often can replace bridges with less disruption. By building the components away from the daily flow of traffic, crews don't have to stick with the normal sequence of construction, says Benjamin Tang, an Oregon Department of Transportation bridge engineer. Add in a basic style with a large nearby footprint and fast-tracking becomes even slicker.

What this new bridge won't do is change the fact that the remaining three spans crossing the Skagit are functionally obsolete. But the chance of a similar failure on these spans remains low, and that's a good thing: America is full of old bridges that need to be replaced.

Tim Newcomb covers infrastructure and sports for Popular Mechanics. Follow him on Twitter at @tdnewcomb.

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